1. Field of the Invention
The present invention is directed to a material separator apparatus wherein changing current in an electromagnet induces an eddy current in materials to be separated. The interaction of the eddy current with the original magnetic field by the Lorentz Force Law will generate a force on the object containing the eddy current. In accordance with Lenz's Law, this current will be in a direction to produce a repulsive force which can be used to alter the trajectory of the object and thus separate it from other materials. The more rapidly the driving current and thus the electromagnet's magnetic field changes the larger the generated eddy currents. Bipolar currents and magnetic fields in which the direction of the field completely changes will have no significant effects on non-ferrous conductive metals since the direction of the eddy current will also change accordingly. In ferrous metals, the repulsion produced by the eddy currents is small compared to the attractive force produced through the flux linkage with the ferrous metal. Reversing the current and the resulting magnetic field in the electromagnet more quickly than in the material to be separated produces a magnetic field of opposite polarity thus repulsing the material. In particular, the present invention makes use of these characteristics and provides a material separation apparatus wherein the rate of change of the alternating current driving an electromagnet is carefully controlled by a microprocessor to maximize the efficiency of the separator process and differentiate materials based on their conductivity and permeability.
2. Prior Art
One use of a material separator apparatus is in the recycling industry. One particular use is to separate materials generated from automobile vehicle refuse.
In one process, old vehicles are crushed and then shredded. The shredded materials will first be passed through an apparatus to remove ferrous metals which make up a significant portion of the metallic components, such as fenders, body materials and the like. The remaining material is then delivered to the present separator to separate non-ferrous metals therefrom.
The use of alternating magnetic fields to induce an eddy current in materials to be separated is well known. An area of rapidly changing high density magnetic flux is produced. As the materials pass through the area, they are subjected to the changing magnetic flux which induces an eddy current. These eddy currents in turn produce a Lorentz Force to change the direction of movement of the material.
At least two general procedures have been employed in the past. One procedure is to use a series of permanent magnets mounted on a rotor which are moved or rotated to produce an alternating magnetic field. The alternating magnetic field induces an eddy current in the materials so that a repulsive magnetic force is produced. A disadvantage of this type of separator is that a fast rotor speed is required to produce the desired eddy current. An example of this type of separator apparatus is shown in Siesco Jr. (U.S. Pat. No. 5,207,330). Another type of separator employs an electromagnet or magnets to produce a magnetic field. Examples of the use of an electromagnet are shown in Sommer Jr. et al. (U.S. Pat. No. 4,069,145), Reid (U.S. Pat. No. 5,064,075) and Benson, et al. (U.S. Pat. No. 3,448,857). The electromagnetic separators typically employ a single frequency (although adjustment of the frequency is possible) using a standard sinusoidal waveform. These electromagnetic separators also employ a unipolar single phase current drive circuit.
It is also known that the strength of the induced eddy current is proportional to the strength of the magnetic field and its rate of change. While it is possible to simply increase the frequency to increase the rate of change, the present invention controls the rate of change by controlling the waveform.
It is, therefore, a principal object and purpose of the present invention to control the alternating current waveform to maximize the eddy current produced and thereby maximize the efficiency of the separator apparatus.